Shri Sant Gajanan Maharaj College of Engineering Department

RF Transformer They are used in electronic circuits that operate between 30 k. Hz

RF Transformer They come with some Impedance ratio between primary and secondary windings e.

RF Transformer They are used as LC tuned circuits. Hence in many models a

RF Transformer They use core that has ferrite as magnetic material. The core is

RF Transformer They are of small size because VA rating is less and voltage

RF Transformer Application RF Amplifier in Radio RF transformer voltages range from milli volt

RF Transformer Application Impedance Matching Network for Antenna Impedance matching ensures maximum power transfer

RF Transformer Application Impedance Matching Network for Antenna An RF Transformer with toroidal winding

RF Transformer Application Mixer – A circuit that gives output that has frequency that

RF Transformer Principle When signal current goes through the primary winding, it generates a

Relation between Z 1 and Z 2 Z 1= Primary winding impedance Z 2=

Impedance Matching Property • When one high frequency circuit is connected with another high

Impedance Matching in Coupled Amplifiers Impedance of first transistor is properly matched with next

Ferrite Core in RF Transformer • Soft ferrites are made from oxides of nickel,

Why Toroid Shaped Core is used in RF Transformer ? Leakage flux is less.

How EMI is reduced in RF Transformer? • The magnetic field of RF transformer

Assembly of RF Transformer • Step –I: Inductances of primary winding and secondary winding

RF Transformer Testing • DC Resistance: Measured by multimeter • Inductances L 1 and

Slides: 27

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Shri Sant Gajanan Maharaj College of Engineering Department of Electronics & Telecommunications Engineering Electronic Devices & Components Unit – II Switches, Relays, Cables, Connectors, Heat Sink, Fuses, Choke, Electronic Transformers Radio Frequency (RF) Transformers

RF Transformer They are used in electronic circuits that operate between 30 k. Hz to 30 MHz

RF Transformer They come with some Impedance ratio between primary and secondary windings e. g. , 1: 4

RF Transformer They are used as LC tuned circuits. Hence in many models a capacitor is connected across the primary winding

RF Transformer They use core that has ferrite as magnetic material. The core is in shape of a Toroid

RF Transformer They are of small size because VA rating is less and voltage rating is few volts and current rating is milli amperes

RF Transformer Application RF Amplifier in Radio RF transformer voltages range from milli volt to few volts. Current range is milliampere

RF Transformer Application Impedance Matching Network for Antenna Impedance matching ensures maximum power transfer from source to load

RF Transformer Application Impedance Matching Network for Antenna An RF Transformer with toroidal winding is seen in image above

RF Transformer Application Mixer – A circuit that gives output that has frequency that is difference between input frequencies

RF Transformer Principle When signal current goes through the primary winding, it generates a magnetic field that induces a voltage across the secondary winding. Connecting a load to the secondary causes an AC current to flow in the load

Relation between Z 1 and Z 2 Z 1= Primary winding impedance Z 2= Secondary winding impedance n = ratio of secondary no. of turns to primary number of turns

Impedance Matching Property • When one high frequency circuit is connected with another high frequency circuit, maximum power is not transferred from one to another • This is due to impedance mismatching • If RF transformer with proper turns-ratio is inserted between the two circuits, maximum power is transferred

Impedance Matching in Coupled Amplifiers Impedance of first transistor is properly matched with next transistor • Hence base terminal of second transistor receives more signal from first stage • Overall gain of this multi-stage amplifier is high •

Ferrite Core in RF Transformer • Soft ferrites are made from oxides of nickel, zinc or magnesium • Have high permeability • Low eddy current loss due to high resistivity • They have low coercivity (ability to resist demagnetization). B-H can reverse immediately, means magnetization can be immediately reversed without much energy. Hence hysteresis losses are low. • Typical parameters Curie Temperature: 140 o. C Permeability: 5000

Ferrite Core B-H curve

Ferrite Cores

Ferrite Material Data

Why Toroid Shaped Core is used in RF Transformer ? Leakage flux is less. Flux concentrates at centre of toroid • Maximum flux utilization • Less electromagnetic interference [EMI] •

How EMI is reduced in RF Transformer? • The magnetic field of RF transformer should not interact with adjacent circuits, otherwise circuit performance will not be reliable • If RF transformer is enclosed in metal can, EMI is reduced • Alloys used to make metal cans have commercial names like Mu-metal and Permalloy

RF Transformer Assembly

Assembly of RF Transformer • Step –I: Inductances of primary winding and secondary winding are determined • Step – 2: Number of turns of primary and secondary windings are calculated • Step 3: On a toroidal core, primary coil is wound, followed by insulating tape, followed by secondary coil and then again insulating tape • Step 4: Coils are lacquered to hold them intact and protect against humidity • Step 5: Contact lugs are attached to windings • Step 6: The ends of windings are given a coating of tin

Assembly of RF Transformer

RF Transformer Testing • DC Resistance: Measured by multimeter • Inductances L 1 and L 2: Inductance of primary and secondary windings is measured by LCR meter • Mutual inductance M: • Coupling Coefficient k: • Quality factor Q: by LCR meter • Bandwidth: By varying frequency and noting output voltage

RF Transformer Data Sheet